1. Technical Field
This invention relates to an optical recording medium having recorded thereon second data, as supplementary data, in addition to first data as main data, a recording method and apparatus for recording the supplementary data along with the main data on this optical recording medium and a method and apparatus for reproducing an optical recording medium having the first and second data recorded thereon. More particularly, this invention relates to an optical recording medium in which the shape of plural pits of a track comprised of the pits representing recording data and lands between these pits is deformed to record other data, a recording method and apparatus for recording data on the optical recording medium and to a method and apparatus for reproducing the optical recording medium.
2. Background Art
Up to now, an optical disc, such as a compact disc with a diameter equal to 12 cm, is widely employed as an optical recording medium having recorded thereon audio data, such as music numbers.
In recording on this optical disc, audio data is sequentially blocked and added to with an error correction code. The resulting data is modulated with EFM (eight to fourteen modulation), with the results of the modulation being recorded by NRZI (non-return-to-zero inverted) modulation. On the compact disc, audio data is recorded by repetition of pits and lands with nine different lengths of the periods of 3T to 11T, where T is the basic period equal to the channel clock period.
The pits formed in the optical disc based on the recorded audio data are of length in the track direction equal to approximately 0.87 to 3.18 μm, in association with the periods of 3T to 11T, with the pit width corresponding to the length in a direction perpendicular to the track direction being approximately 0.5 μm, with its depth being approximately 0.1 μm.
Meanwhile, in a compact disc, audio data is recorded in a frequency range of 20 Hz to 20 kHz. However, a demand is raised to enable audio data to be recorded over a broader frequency range to realize audio reproduction of a higher sound quality. There is also raised a demand for recording audio data of three or more channels, instead of two channels, that is left and right channels, to enable variegated audio reproduction, such as surround reproduction.
Moreover, there is raised a demand for enabling audio data recorded on an optical disc to be reproduced only under a pre-set condition to protect the recorded audio data.